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Alert Notice 221: Fading of 2007+20 FG Sge AND Request to monitor 2138+43 SS Cyg for observations with HST, EUVE, and RXTE AND 1058+38 Markarian 421 in outburst AND Activity of 1814+39 AM Her continues AND 1746-17 -- Sgr is a new planetary-nebula nucleus

We have been informed by the Central Bureau for Astronomical Telegrams that
S. Shugarov, Sternberg Astronomical Institute, Moscow, reported that FG Sge,
the central star of a planetary nebula, has faded dramatically to approximately
V magnitude 16 and B magnitude 17 on April 24.04 UT (IAU Circular 6323). Our
member Monsignor Ron Royer has confirmed the fading and his CCD observations
made with IR-blocking filter indicated that this star was at magnitude 16.0 on
May 7.3556 UT.

FG Sge started to decline from its about 25-year long average maximum magnitude
of 9.2 in August 1992. By October 1992 it reached magnitude 13.7 (see AAVSO
Alert Notice 163). Since then, it has brightened to magnitude 10.2 several
times but has never fully reached maximum, and has faded, reaching as faint as
magnitude 14.4 in August 1994.

Recent observations indicate that in January 1996 it reached 10.2 and started
to fade slowly, as shown by the observations below. The current magnitude is
the faintest FG Sge has been since 1894 (see AAVSO Alert Notice 163). Recent
observations include:

There are two very close stars to the east of FG Sge. Observers should be
aware of these stars. The star about 8 - 10 arcseconds east is a suspected
variable; R. Royer reported this star to be at magnitude 12.3 on May 7.3556 UT.
The star to the east of this suspected variable was reported by Royer at
magnitude 15.0 on May 7.3556 UT. J. Bortle informs us that the apparent
magnitude of FG Sge is very strongly influenced by its close companion. He
recommends that high magnification (several hundred times) be employed in
making estimates. One must not only resolve the pair, but the pair must also
appear well separated before a proper brightness determination can be made.

Accompanying is a CCD image provided by R. Royer, which shows the very faint
FG Sge together with its two companion stars to the east. Also accompanying
is the AAVSO 'e' scale preliminary chart for FG Sge prepared by C. Scovil.
The companion star suspected as variable is indicated as 'var?' on the chart,
and is located closer to FG Sge than can be accurately indicated on the chart.
Observers with large-aperture telescopes and those with CCDs are strongly urged
to monitor FG Sge and call in your observations to AAVSO Headquarters.

Also accompanying is a light curve of FG Sge since 1985, showing its maximum
phase as well as the decline since 1992; we have also placed this light curve
on our ftp site. 157 AAVSO observers contributed 5,544 observations to this
light curve; we acknowledge each observer's contribution with gratitude.

REQUEST TO MONITOR 2138+43 SS CYGNI FOR OBSERVATIONS WITH HST, EUVE, AND XTE

We are collaborating with astronomers from Lawrence Livermore National
Laboratory in the observations of SS Cyg in an exciting observing program that
will involve the Hubble Space Telescope (HST), Extreme Ultraviolet Explorer
(EUVE), and the X-ray Timing Explorer (XTE). From now until the end of
December, these three satellites have been scheduled to observe SS Cyg as a
target-of-opportunity object during a maximum, in search of very small-
amplitude and very short-period oscillations of the white dwarf.

In order to be able to carry out these observations, we have been requested to
inform the investigating astronomers when SS Cyg starts to go into outburst,
i.e., brightens, and to continue to keep them informed throughout the outburst
so that these satellites may be scheduled to observe SS Cyg.

Small-amplitude, short-period, coherent oscillations with a period of 7.5
seconds were obtained during outburst for SS Cyg by R. Hildebrand and his
colleagues in the late 1970's and early 1980's. We assisted them in these
observations while they were observing several dwarf novae with ground-based
telescopes. However, this particular study has not been carried out using
multiple satellites and multiwavelength observations, thus the current study
will be a pioneering one in the study of small-amplitude, short-period
oscillations of the white dwarf in dwarf novae-type cataclysmic variables.
The success of these observations very much depends on your observations and
the early alerts and continuous information we can provide to our colleagues.

Presently, SS Cyg is fading slowly from an outburst, as indicated by the
following observations:

Please monitor SS Cyg closely, and inform us by phone, fax, or email when it
starts to brighten, i.e., becomes brighter than 11.5. Once SS Cyg goes into
outburst, please send in your observations daily so we may keep the astronomers
informed regarding this very interesting star.

1058+38 MARKARIAN 421 IN OUTBURST

We have been informed by Dr. J. Pesce, Space Telescope Science Institute,
that the Whipple Gamma Ray Collaboration has reported an extraordinary
outburst of gamma-ray activity from Markarian 421 (see AAVSO Alert Notice 220).
P. Garnavich, observing with the Whipple 1.2-m optical telescope, has detected
brightening of 0.25 magnitude in the R band in this object containing an active
galactic nucleus.

Please continue to monitor Markarian 421 closely, and report your observations
to AAVSO Headquarters. Accompanying is a revised 'e' scale AAVSO preliminary
chart prepared by C. Scovil of Markarian 421: the position of this object has
been revised and additional comparison stars have been added.

ACTIVITY OF 1814+39 AM HERCULIS CONTINUES

The magnetic variable AM Her continues to fade very slowly, as indicated by
the following observations:

If AM Her is indeed fading and reaches its down state, multiwavelength
observations will be carried out as an international observing campaign (see
AAVSO Alert Notice 220).

Please continue to monitor AM Her and report your observations to AAVSO
Headquarters.

1746-17 -- SGR IS A NEW PLANETARY-NEBULA NUCLEUS IN SAGITTARIUS

The Central Bureau for Astronomical Telegrams announced (IAU Circular 6322)
that S. Nakano, Sumoto, Japan, reported the discovery by Yukio Sakurai,
Otsuka-cho, Mito, Ibaraga-ken, Japan, of an object thought to be a possible
slow nova on Feb 20.806 UT, using Fuji G400 film and a 300-mm f/2.8 lens. The
object was red and of photographic magnitude 11.4. Patrol films Sakurai took
in 1993 and 1994 showed no object, but it was visible at about magnitude 12.5
on films beginning in January 1995.

This object is in fact the nucleus of a planetary nebula, and is similar to
V605 Aql, according to private communication we have received from H. Bond of
the Space Telescope Science Institute. He writes, "V605 Aql was bright for
several years around 1919, and the outburst was probably a late helium shell
flash occurring in a massive white dwarf. It would be very important for the
AAVSO to observe the outburst of [-- Sgr] over the next several years. If
similar to V605 Aql, it will continue to brighten for a year or two, and then
fade away over a similar timescale..."

Accompanying is a 'd' scale AAVSO preliminary chart of -- Sgr prepared by
C. Scovil. Please add -- Sgr to your observing program if it is within the
reach of your telescope and monitor it, and report your observations to AAVSO
Headquarters with your regular monthly reports. If you see any sudden change
in brightness or behavior, please phone/fax/email your observations to us.

The answering machine at AAVSO Headquarters is on nights and weekends for your
convenience. Please call our charge-free number (800-642-3883) to report your
observations. We also encourage observers to send observations by fax to
617-354-0665 or by e-mail through the Internet to observations@aavso.org. We
would appreciate it very much if you would report your observations in
Universal Time.

Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

Janet A. Mattei
Director

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